Modified oxime extractant formulation

ABSTRACT

A solvent extraction composition that is particularly useful for the extraction of metals from a solution containing the metals. The solvent extraction composition includes an orthohydroxyaryloxime extractant, at least one water immiscible organic solvent, and an effective amount of a substantially water insoluble equilibrium modifier. The equilibrium modifier includes at least one of an aliphatic, aromatic or araliphatic compound comprising three or more ester functional groups. A method for the solvent extraction of a metal such as copper from an aqueous solution using the solvent extraction composition is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Patent Application No. 61/792,832, filed Mar. 15, 2013, entitled “MODIFIED OXIME EXTRACTANT FORMULATION,” which is incorporated herein by reference in its entirety.

FIELD

This disclosure relates to the field of metals extraction from solutions containing the metals, and in particular relates to the field of solvent extraction compositions for the recovery of copper that include an oxime compound and an equilibrium modifier.

BACKGROUND

The starting material for large-scale solvent exaction processing of metals such as copper is an aqueous leach solution—usually a sulfuric acid solution, but it may also be a basic aqueous solution when ammonia is the leaching agent—that is distributed over mined ore containing a mixture of metals in addition to copper, dissolving salts of copper and other metals as the leach solution trickles through that ore.

The aqueous leach solution with its resulting mixture of metal values (e.g., solubilized metal values) is then mixed in mixer tanks with a water-immiscible, liquid hydrocarbon solvent (e.g., kerosene) containing one or more extractant chemicals (e.g., oximes), possibly including one or more equilibrium modifiers, that selectively form a metal-extractant complex or chelate with the copper ions/values in preference to ions of other metals, in a step called the extraction or loading stage of the solvent extraction process. The outlet of such tanks continuously feeds to a large settling tank, where the organic solvent (organic phase), now containing the copper-extractant complex in solution, is separated from the copper-depleted aqueous solution (aqueous phase) in a phase separation stage.

This phase separation stage may be complicated by the presence of such equilibrium modifiers in the extractant formulation, which may hinder phase separation and/or may cause the build-up of crud (a solid stabilized emulsion) at the boundary of the phases. At higher concentrations of modifier(s) in the extractant formulation, the modifier contributes significantly to the viscosity of the overall reagent formulation, and therefore, being able to use less of the modifier is an advantage because the overall viscosity of the organic phase will also be lower—a particularly important advantage in the phase separation stages.

After extraction and phase separation, the metal-depleted aqueous feedstock (raffinate) is either discharged or recirculated to the ore body for further leaching. The loaded organic phase, now pregnant with the dissolved copper-extractant complex, is fed, possibly after a washing stage to facilitate removal of undesired amounts of iron and other metal ions, to a stripping stage, comprising another set of mixer tanks, where it is mixed with an aqueous sulfuric acid strip solution. This strip solution breaks apart the copper-extractant complex and permits the extracted copper to pass to another settler tank for another phase separation, where, again, equilibrium modifiers may cause inefficient phase separation and undesired entrainment of the organic phase in the resulting strip aqueous phase.

On the other hand, however, adding a limited quantity of one or more equilibrium modifiers to the extractant formulation shifts the equilibria in such a manner that one can efficiently strip higher amounts of copper from the extractant using conventional stripping solutions, generating a more copper-rich electrolyte, well suited for the electrodeposition of high purity copper.

From the stripping settler, the “regenerated” organic phase, partially stripped of its metal values, is recycled to the extraction mixers to begin extraction again, and the copper-rich strip aqueous phase is customarily fed to an electrowinning tankhouse, where the copper metal values are collected on plates by a process of electrodeposition. Then, after electrowinning to harvest the copper values from the aqueous solution, the copper-depleted solution, known as spent electrolyte, is returned to the stripping mixers to begin stripping again.

Modifiers of extraction and stripping equilibria are frequently incorporated in the commercial reagent formulations, with particular utility when such formulations include the so-called “strong” extractants, e.g., the aldoximes. Such extractants are capable of forming a very stable complex association with copper at quite low pH's and, consequently, require the use of very highly acidic aqueous stripping solutions in order to effect the breakdown of the copper-extractant complex. The resultant copper-rich aqueous strip solution, however, is not suitable for the electrowinning of high purity copper metal due to the high acid concentration and the relatively low copper concentration, since the solubility of copper sulfate is depressed at high sulfuric acid concentrations.

The use of modified aldoximes (i.e., an aldoxime extractant plus an equilibrium modifier) and aldoxime/ketoxime blends to extract copper from aqueous acidic sulfate solutions is well known. ICI introduced P5100, 5-nonylsalicylaldoxime (NSO) modified by nonylphenol (NP), to the industry in the early 1980's, then Henkel introduced LIX 622, a mixture of isotridecyl alcohol (TDA) with 5-dodecylsalicylaldoxime, and LIX 622N, TDA in combination with NSO. U.S. Pat. Nos. 4,978,788; 5,176,843; 5,281,336; 6,113, 804; and 6,277,300 (all by Dalton et al. and incorporated herein by reference in their entirety) describe formulations based on the use of lightly-branched alcohols and esters, such as 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (“TXIB”), as modifiers. U.S. Pat. No. 6,177,055 by Virnig et al., which is incorporated herein by reference in its entirety, discloses the use of linear esters, such as di-n-butyl adipate (DBA), as modifiers. U.S. Pat. No. 6,231,784 by Virnig et al., which is and incorporated herein by reference in its entirety, discloses a very broad range of chemical classes, including simple carboxylic acid esters, oximes, nitriles, ketones, amides (e.g., carboxamides, sulfonamides and/or phosphoramides), carbonates, carbamates, sulfoxides, ureas, phosphine oxides, alcohols, ester ethers, polyethers and mixtures thereof, that can be used in combination with the NSO aldoxime to formulate copper solvent extraction reagents. Other chemical classes besides esters showed equal or greater ability to modify the copper affinity of oximes. In practice, however, esters have proved to have the best combination of reducing copper affinity and allowing efficient operation of extraction processes.

Two articles providing analysis of the effects of modified oxime exaction reagents on the extraction and recovery process are: “Discussion of the Physiochemical Effects of Modifiers on the Extraction Properties of Hydroxyamines; A Review”, A. M. Sastre and J. Szymanowski, Solvent Extraction and Ion Exchange, Vol. 22(5), pp 737-759 (2004); and “Equilibrium Modifiers in Copper Solvent Exaction Reagents—Friend or Foe?”, G. Kordosky and M. Viring, Proceedings of Hydromet 2003, TMS, 2003.

SUMMARY

The currently-used equilibrium modifiers require fairly high modifier concentrations relative to the one or more oxime extractants in order to achieve the desired modifying effect. These high concentrations increase the overall cost of the solvent extractant composition and increase the adverse effects of the modifiers, such as increased viscosity in the organic phase and increased density of the organic phase, both of which contribute to poor phase separation and/or crud generation in the mixer/settlers. Accordingly, one objective is to provide equilibrium modifiers which deliver effective levels of modification at lower ratios of modifier-to-oxime extraction reagent(s).

In one embodiment a solvent extraction composition is provided. The composition includes:

an orthohydroxyaryloxime extractant;

at least one water immiscible organic solvent; and

an effective amount of a substantially water insoluble equilibrium modifier selected from the group consisting of aliphatic, aromatic, and araliphatic compounds, the equilibrium modifier comprising three or more ester functional groups.

In one characterization of this embodiment, the orthohydroxyaryloxime extractant comprises a compound according to Formula (1):

and salts, tautomers or metal complexes thereof, wherein R¹ is an optionally substituted C₁-C₂₀ hydrocarbyl group and R² is an optionally substituted C₆-C₂₀ orthohydroxyaryl group.

In another characterization of the solvent extraction composition, the orthohydroxyaryloxime extractant comprises a compound according to Formula (2):

and salts, tautomers or metal complexes thereof, wherein R³ is an optionally substituted C₆-C₂₀ orthohydroxyaryl group.

In another characterization, the orthohydroxyaryloxime extractant comprises a compound selected from the group consisting of: 5-(C₈ to C₁₄ alkyl)-2-hydroxyacetophenone oximes, 5-(C₈ to C₁₄ alkyl)-2-hydroxybenzaldoximes, and mixtures thereof.

In another characterization, the equilibrium modifier comprises up to 80 carbon atoms.

In another characterization, the ester functional groups comprise butyrates, propanates and mixtures thereof.

In another characterization, the equilibrium modifier is selected from the group consisting of trihydroxy alcohols, tetrahydroxy alcohols, polyhydroxy compounds, tricarboxylic acids, tetracarboxylic acids and mixtures thereof.

In another characterization, the equilibrium modifier comprises a trihydroxy alcohol. For example, the trihydroxy alcohol may comprise up to 20 carbon atoms and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms. Further, the trihydroxy alcohol may be selected from the group consisting of: glycerol; 1,1,1-tris(hydroxymethyl)propane; 1,1,1-tris(hydroxymethyl)ethane; 1,2,6-hexanetriol; 3-methyl-1,3,5-pentanetriol; 1,3,5-triazine-2,4,6-triol; 1,2,4-butanetriol; 1,3,5-trihydroxybenzene; pyrogallol; and isomers of these compounds.

In another characterization, the equilibrium modifier comprises a tetrahydroxy alcohol. For example, the tetrahydroxy alcohol may comprise up to 20 carbon atoms and a optionally substituted monocarboxylic acid containing 1-20 carbon atoms. In one particular characterization, the tetrahydroxy alcohol is selected from the group consisting of pentaerythritol and erythritol.

In another characterization, the equilibrium modifier comprises a polyhydroxy compound. For example, the polyhydroxy compound comprises 5 or more alcohol functional groups having up to 40 carbon atoms and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms. The polyhydroxy compound may be selected from the group consisting of dipentaerythritol, carbohydrates and carbohydrate polyols. The polyhyroxy compound may be selected from the group consisting of monosaccharide, disaccharide, oligosaccharide and polysaccharide. The equilibrium modifier may comprise a mixture of at least one carbohydrate and at least one carbohydrate polyol, mannitol, sorbitol, xylitol, lactitol, maltitol, erythritol, isomalt, 1,6-GPS, 1,1-GPS, 1,1-GPM, hydrogenated starch hydrolyzate, hydrogenated glucose syrup and mixtures thereof. The equilibrium modifier may comprise a carbohydrate polyol selected from the group consisting of a C₅-polyol, a C₆-polyol and mixtures thereof. The equilibrium modifier may comprise a disaccharide polyol, for example where the disaccharide polyol may be selected from the group consisting of arabitol, xylitol, ribitol, inositol, mannitol, sorbitol, galactitol, and mixtures thereof.

In another characterization, the equilibrium modifier may comprise a tricarboxylic acid. For example, the tricarboxylic acid may comprise up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms. The tricarboxylic acid may be selected from the group consisting of: benzene-1,2,4-tricarboxylic acid; trimesic acid; tricarballylic acid; aconitic acid; and mixtures thereof.

In another characterization, the equilibrium modifier comprises a tetracarboxylic acid. For example, the tetracarboxylic acid may comprise up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms. The tetracarboxylic acid may be 1,2,4,5-benzenetetracarboxylic acid.

In another characterization, the equilibrium modifier compound comprises alcohol functional groups that have been ethoxylated, propoxyated, or ethoxylated and propoxylated.

In another characterization, the equilibrium modifier has a ratio of carbon atoms to ester functional groups of from about 7:1 to about 3:1, such as from about 6:1 to 4:1.

In another characterization, the equilibrium modifier comprises at least one ether functional group or alcohol functional group. For example, a ratio of carbon atoms to oxygen atoms in such a modifier may be from about 3.5:1 to about 2:1.

In another characterization, the molar ratio of the orthohydroxyaryloxime extractant to the equilibrium modifier is at least about 0.02, and is not greater than about 1.5.

In another characterization, the composition comprises at least about 1 wt. % and not greater than about 70 wt. % of the orthohydroxyaryloxime extractant, such as at least about 5 wt. % and not greater than about 30 wt. % of the orthohydroxyaryloxime extractant.

In another characterization, the orthohydroxyaryloxime extractant comprises a mixture of aldoxime and ketoxime, such as where the weight ratio of the aldoxime:ketoxime is from about 90:10 to about 30:70.

In another characterization, the organic solvent has an aromatic hydrocarbon content of not greater than about 30 wt. %, for example not greater than about 23 wt. %.

In another characterization, the solvent extraction composition comprises at least about 30 wt. % and not greater than about 95 wt. % of the organic solvent.

In another characterization, the solvent extractant composition may further comprise an anti-degradation additive, such as at least about 0.1 wt. % and not greater than about 10 wt. % of an anti-degradation additive.

The foregoing compositions are particularly useful for the solvent extraction of one or more metals from a solution, such as an acidic solution containing the metals. Thus in one embodiment, a process for recovering a metal from an aqueous solution is provided. The method comprises the steps of:

contacting an aqueous solution containing a metal with a solvent extraction composition according to the foregoing embodiment and any of its characterizations, thereby forming a metal-solvent extractant complex in a water-immiscible phase, and contacting the metal-solvent extractant complex in the water-immiscible phase with an aqueous acidic strip solution, thereby stripping the metal from the water-immiscible phase.

In one characterization, the aqueous solution may be an acidic solution. The metal may be chosen from the group consisting of copper, iron, cobalt, nickel, manganese, zinc and mixtures thereof.

In another characterization, the volume ratio of solvent extractant to aqueous acidic solution may be from about 20:1 to about 1:20, such as from about 5:1 to about 1:5.

In another characterization, the process further comprises the step of recycling the solvent extractant or the aqueous acidic solution.

The aqueous acidic strip solution may be a mineral acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid and mixtures thereof.

DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an example of an improvement in modifier strength of modifier formulations disclosed herein.

DESCRIPTION

The terms “equilibrium modifier”, “modifier” and “thermodynamic modifier” are used interchangeably herein to generally refer to additives for an extractant reagent, which reagent may comprise one or more oxime extractants. The use of such equilibrium modifiers materially increases the net copper transfer from the extraction stage to the stripping stage in the organic phase. In one aspect, the present disclosure provides ester equilibrium modifiers where the compounds contain three or more ester functional groups. These compounds are herein termed polyesters.

In one aspect, the present disclosure provides solvent extraction compositions comprising a mixture of an extractant reagent (e.g., comprising one or more orthohydroxyaryloxime extractants, such as blends of ketoximes and aldoximes) and an organic solvent, in combination with one or more polyester equilibrium modifiers. The equilibrium modifiers may be used in an amount and in a molar ratio of equilibrium modifier(s) to extractant reagent that is effective to provide a net copper transfer that is greater than the net copper transfer that is achieved by extraction with the extractant reagent(s) alone, i.e., in the absence of the modifier(s). The solvent extraction composition may optionally include one or more known equilibrium modifiers in addition to the polyester equilibrium modifiers disclosed herein.

In a further aspect, this disclosure provides a process for extracting metal values such as copper ions/values from aqueous leach solutions (e.g., acidic solutions) containing copper ions/values. For example, the process may include the steps of:

(a) contacting an aqueous (e.g., acidic) solution containing a metal (e.g., copper) with an organic solvent extraction composition comprising a water-immiscible liquid hydrocarbon solvent solution of a solvent extraction composition comprising one or more oxime extraction reagents, and one or more polyester equilibrium modifiers, to extract at least a portion of the copper values from the aqueous solution (e.g., resulting in a largely copper-barren aqueous phase) into the organic phase (e.g., resulting in a copper-pregnant organic phase);

(b) separating the copper-pregnant organic phase from the copper-barren aqueous phase; and

(c) recovering the copper values from the copper-pregnant organic phase.

Extractant Reagent

The extractant reagent may include an oxime reagent, and in particular may comprise an orthohydroxyaryloxime extractant. Particularly useful among these compounds may be aldoxime extractants, ketoxime extractants, or combinations thereof.

By way of example, the extractant reagent may comprise an orthohydroxyaryloxime compound according to Formula (1):

such as where R¹ is an optionally substituted C₁-C₂₀ hydrocarbyl group and R² is an optionally substituted C₆-C₂₀ orthohydroxyaryl group. Salts, tautomers or metal complexes of this compound may also be useful.

Another example of an extractant reagent comprises a compound according to Formula (2):

where R³ is an optionally substituted C₆-C₂₀ orthohydroxyaryl group. Salts, tautomers or metal complexes of this compound may also be useful.

In one particular characterization, the orthohydroxyaryloxime extractant comprises a compound selected from the group consisting of: 5-(C₈ to C₁₄ alkyl)-2-hydroxyacetophenone oximes, 5-(C₈ to C₁₄ alkyl)-2-hydroxybenzaldoximes, and mixtures thereof.

Other examples of oxime reagents are disclosed in U.S. Pat. No. 7,993,613 by Virnig, U.S. Pat. No. 6,277,300 by Dalton et al., and U.S. Pat. No. 8,329,124 by Campbell et al. The disclosure of each of these patents is incorporated herein by reference in its entirety.

In one particular characterization, the orthohydroxyaryloxime extractant may include a mixture of an aldoxime and a ketoxime. For example, the orthohydroxyaryloxime extractant may include a mixture of aldoxime and ketoxime where the weight ratio of the aldoxime:ketoxime is from about 90:10 to about 30:70, e.g., is not greater than about 90:10 and is at least about 30:70.

Organic Solvents

A wide variety of essentially-water-immiscible, water-insoluble liquid hydrocarbon solvents may be used in the solvent extraction compositions. These include aliphatic and aromatic hydrocarbons, such as kerosene, benzene, toluene, xylene, and the like. The selection of essentially water-immiscible liquid hydrocarbon solvents, or mixtures thereof, for commercial operations will depend on a number of factors, including the design of the solvent extraction plant (mixer-settler units, Podbielnak extractors, and the like). Particularly useful solvents for copper recovery processes may be selected from essentially-chemically-inert aliphatic and aromatic hydrocarbons having flash points of 130° F. (54° C.) and higher, and preferably at least 150° F. (66° C.), and solubilities in water of less than 0.1%, by weight. Representative commercially-available solvents are Chevron ion exchange solvent, available from Standard Oil of California, having a flash point 195° F. (91° C.); Escaid 100 and 110, available from Exxon-Europe, having a flash point of 180° F. (82° C.); Norpar 12, available from Exxon-USA, with a flash point of 160° F. (71° C.); Conoco™-C1214, available from Conoco, with a flash point of 160° F. (71° C.); Aromatic 150, an aromatic kerosene available from Exxon-USA, with a flash point of 150° F. (66° C.); and other kerosene and petroleum fractions available from various oil companies.

In one particular characterization, the organic solvent is selected to have an aromatic hydrocarbon content of not greater than about 30 weight %, such as not greater than about 23 weight %, such as not greater than about 10 weight % or even not greater than about 5 weight %.

The solvent extraction composition may include at least about 30 weight % of the organic solvent. In another characterization, the solvent extraction composition may include not greater than about 95 weight % of the organic solvent. For example, the solvent extractant composition may include at least about 5 weight % and not greater than about 25 weight % of the organic solvent.

Equilibrium Modifiers

In one characterization of the solvent extraction compositions disclosed herein, the equilibrium modifier includes an organic compound having multiple ester functional groups, and in particular having three or more ester functional groups. The equilibrium modifiers may be substantially water insoluble. In one characterization, the organic compound comprising the ester functional groups is selected from the group consisting of aliphatic, aromatic, and araliphatic compounds.

The ester functional groups may comprise butyrates, propanates, and the like, as well as combinations of different esters. According to one embodiment, the equilibrium modifier may be selected from the group consisting of trihydroxy alcohols, tetrahydroxy alcohols, polyhydroxy compounds, tricarboxylic acids, tetracarboxylic acids and mixtures thereof. The equilibrium modifier may, for example, comprise up to 80 carbon atoms.

It may be desirable to control the ratio of carbon atom to ester functional groups in the equilibrium modifier. In one characterization, the ratio of carbon atoms to ester functional groups is not greater than about 7:1, such as not greater than about 6:1. Further, in another characterization, the ratio of carbon atoms to ester functional groups is at least about 3:1, such as at least about 4:1. Thus, in one characterization, the ratio of carbon atoms to ester functional groups is from about 7:1 to about 3:1. In another characterization, the ratio of carbon atoms to ester functional groups is from about 6:1 to about 4:1.

Further, in some characterizations, the equilibrium modifier may comprise at least one ether functional group or alcohol functional group. In this regard, the ratio of carbon atoms to oxygen atoms may be controlled, for example so that the ratio of carbon atoms to oxygen atoms is at least about 2:1 and is not greater than about 3.5:1.

In one characterization, the equilibrium modifier comprises a trihydroxy alcohol. For example, the the trihydroxy alcohol may include up to 20 carbon atoms, and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms. Some examples of trihydroxy alcohols include: glycerol; 1,1,1-tris(hydroxymethyl)propane; 1,1,1-tris(hydroxymethyl)ethane; 1,2,6-hexanetriol; 3-methyl-1,3,5-pentanetriol; 1,3,5-triazine-2,4,6-triol; 1,2,4-butanetriol; 1,3,5-trihydroxybenzene; pyrogallol; and isomers of these compounds.

In another characterization, the equilibrium modifier comprises a tetrahydroxy alcohol. For example, the tetrahydroxy alcohol may include up to 20 carbon atoms and anoptionally substituted monocarboxylic acid containing 1-20 carbon atoms. Particularly useful examples of tetrahydroxy alcohols include pentaerythritol and erythritol, such as where the equilibrium modifier is pentaerythritol propionate.

In another characterization, the equilibrium modifier comprises a polyhydroxy compound. For example, the polyhydroxy compound may include 5 or more alcohol functional groups having up to 40 carbon atoms and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms. Some examples of polyhydroxy compounds include dipentaerythritol, carbohydrates and carbohydrate polyols, such as monosaccharides, disaccharides, oligosaccharides and polysaccharides. The equilibrium modifier may also comprise a mixture of at least one carbohydrate and at least one carbohydrate polyol, mannitol, sorbitol, xylitol, lactitol, maltitol, erythritol, isomalt, 1,6-GPS, 1,1-GPS, 1,1-GPM, hydrogenated starch hydrolyzate, hydrogenated glucose syrup and mixtures thereof. In a further characterization, the equilibrium modifier may include a carbohydrate polyol selected from the group consisting of a C₅-polyol, a C₆-polyol and mixtures thereof, and in a particular characterization the equilibrium modifier may comprise a disaccharide polyol, such as a disaccharide polyol selected from the group consisting of arabitol, xylitol, ribitol, inositol, mannitol, sorbitol, galactitol, and mixtures thereof.

In another characterization, the equilibrium modifier comprises a tricarboxylic acid. For example, the tricarboxylic acid may comprise up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms. Examples of tricarboxylic acids include those selected from the group consisting of: benzene-1,2,4-tricarboxylic acid; trimesic acid; tricarballylic acid; aconitic acid; and mixtures thereof.

In another characterization, the equilibrium modifier comprises a tetracarboxylic acid. For example, the tetracarboxylic acid may comprise up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms. An example of such a tetracarboxylic acid is 1,2,4,5-benzenetetracarboxylic acid.

Any of the foregoing equilibrium modifier compounds may include alcohol functional groups that have been ethoxylated, propoxyated, or both ethoxylated and propoxylated.

In developing solvent extraction compositions for the recovery of copper from leach liquors, it is advantageous to use a reduced (e.g., minimum) amount of equilibrium modifier(s) required to give the desired effect. See “Equilibrium Modifiers in Copper Solvent Extraction Reagents—Friend or Foe?” G. Kordosky and M. Viring, Proceedings of Hydromet 2003, TMS, 2003. It is also desirable to increase (e.g., maximize) the net transfer of copper on the solvent extraction composition, dependent on a combination of the extractive strength of the solvent extraction composition and the ease with which the copper may be stripped.

The use of the foregoing compounds as equilibrium modifiers in a solvent extraction composition advantageously may enable a decreased concentration of the modifier to be used in the compositions.

In one characterization, the molar ratio of the orthohydroxyaryloxime extractant to the equilibrium modifier in the solvent extractant composition is at least about 0.02. In another characterization the molar ratio of the orthohydroxyaryloxime extractant to the equilibrium modifier in the solvent extraction composition is not greater than about 1.5. In another characterization, the solvent extraction composition includes at least about one weight % of the orthohydroxyaryloxime extractant, such as at least about 5 weight % of the orthohydroxyaryloxime extractant. Further, the solvent extraction composition may include not greater than about 70 weight % of the orthohydroxyaryloxime extracting, such as not greater than about 30 weight % of the orthohydroxyaryloxime extractant.

Other Additives

The solvent extraction composition may include other additives in addition to the foregoing compounds. For example, the compositions may include an anti-degradation additive, such as from about 0.1 wt. % to about 10 wt. % of an anti-degradation additive. Examples of anti-degradation additives are disclosed in U.S. Pat. No. 8,329,124 by Campbell et al., which is incorporated herein by reference in its entirety.

Processes for Metal Recovery

The solvent extraction compositions disclosed herein are particularly useful for recovering a metal such as copper from an aqueous solution comprising the metal. For example, the process may include contacting an aqueous solution, such as an acidic aqueous solution containing the metal with the solvent extraction composition. The contacting step will form a metal-solvent extractant complex in a water-immiscible phase. This metal-solvent extractant complex may then be contacted with an aqueous acidic strip solution to strip the metal from the water-immiscible phase.

Although it is contemplated that the aqueous solution will predominantly include copper, other metals such as iron, cobalt, nickel, magnesium, zinc and others may be present within the aqueous solution. The volume ratio of the solvent extracted to the aqueous acidic solution may be from about 20:1 to about 1:20, such as from about 5:1 to about 1:5.

Either or both of the solvent extractant or the aqueous acidic solution may be recycled to conserve reagents. The aqueous acidic strip solution may include a mineral acid, such as a mineral acid selected from a group consisting of sulfuric acid, nitric acid, hydrochloric acid and mixtures thereof. An example of such a solvent extraction process is disclosed, for example, in U.S. Pat. No. 4,039,405 by Wong, which is incorporated herein by reference in its entirety.

Examples

One way to evaluate the effects of different levels of equilibrium modifiers on the metallurgical performance of solvent extraction compositions is to compare the relative measures of the equilibrated strip points of an organic solution of the extractant at a set maximum copper load, which provides a measure of the active oxime content of the extractant. As with the degree of modification, comparison of the relative equilibrated strip points allows comparison of the relative extractive strengths of two extractant formulations. Formulations having lower equilibrated strip points will give superior copper net transfer in a circuit, assuming all other factors, such as circuit configuration, aqueous feed solution, copper loading, and strip solution, are substantially identical.

The strip isotherm point shows the amount of copper in the organic phase when the organic phase, comprising of 0.188M 5-nonylsalicylaldoxime and 30 g/L of modifier dissolved in Escaid 200, an aliphatic kerosene, is contacted with an equal volume of strip aqueous phase containing 30 g/L copper and 170 g/L of sulfuric acid. The strip isotherm point for formulations prepared using various modifiers was incorporated into a QSAR determination of activity:

Modifier strength=f(ester group concentration, number of branches, number of carbon atoms).

The obtained equation may be utilized to elucidate structures that provide unexpectedly good activity for modifying copper affinity. Many of these compounds are not commercially available.

A lower amount of copper remains after stripping solvent extractant compositions incorporating the equilibrium modifiers disclosed herein. This improved stripping performance allows processes to obtain higher copper recoveries. It is unexpectedly observed that molecules with 3 or more ester functional groups and with certain ratios of carbon atoms to ester functional groups (e.g., as is disclosed above) provide superior performance to those currently known or used in the art (e.g., TXIB in Comparative Example 1 of Table I).

For compounds with no ether or unreacted alcohol functional groups, the ratio of carbons atoms to ester functional groups may be from about 7:1 to about 3:1 to provide superior performance to what is currently known in the art (e.g., TXIB). Compounds with C:ester ratios higher than the specified range, such as exhibited by pentaerythritol tetraoctylate (Table I, Comparative Example 2), may have poorer modification performance. Compounds that have C:ester ratios lower than the specified range (e.g., glycerol triformate in Comparative Example 3) are too water soluble to conduct the test. To enhance performance and reduce loss of modifier to the strip solution, the range of C:ester may be from about 6:1 to about 4:1.

Polyester modifiers with ether linkages also show surprisingly good performance. Example 11 in Table I below shows an example of a molecule in this class. The propoxyalted sorbitol hexabutyl ester provides much improved strippability compared with the TXIB modifier. For compounds with 3 or more ester groups and at least one ether or alcohol group, the ratio of C:O atoms may be from about 3.5:1 to about 2:1. A comparison of modifier strength between TXIB and various modifiers disclosed herein is illustrated in Table I.

TABLE I [Cu] in Ester stripped functional C:ester C:O extractant Example Compound groups Ratio Ratio (gpl) Baseline No modifier 0 2.87 Comparative TXIB 2 8 4 1.70 Example 1 Comparative Pentaerythritol 4 9.25 4.6 1.77 Example 2 tetraoctylate Comparative glycerol 3 2 1 too water Example 3 triformate soluble Example 4 Trimethylol- 3 6 3 1.43 propane tributyrate Example 5 Glycerol 3 5 2.5 1.34 triisobutyrate Example 6 Pentaerythritol 4 5.25 2.4 1.37 tetrabutyrate Example 7 Xylitol 5 5 2.6 1.47 pentabutyrate Example 8 Xylose 4 5.25 2.3 1.40 tetrabutyrate Example 9 Pyromellitic acid, 4 6.5 3.25 1.51 tetrabutyl ester Example 10 Dipentaerythritol 6 4.7 2.2 1.31 hexapropanate Example 11 Propoxyalted 6 8 2.7 1.32 sorbitol hexabutyl ester

FIG. 1 illustrates that a 44% improvement in modifier strength can be achieved using a solvent extractant composition disclosed herein (Example 5) as compared to a prior art composition (comparative Example 1).

In one example, pentaerythrytol tetrapropropionate is prepared by reacting 13.6 g of pentaerythrytol (Aldrich) with 62.0 g of proprionic anhydride (Aldrich). A drop of acid is used to catalyze the reaction. The reaction is heated to 70° C. for 3 h to ensure complete esterification. Proprionic acid and residual anhydride is removed by washing with aqueous sodium carbonate. After drying in vacuum, 31.5 g of tetraproprionate is isolated.

The Net Cu Transfer is determined for modified nonylphenolaldoxime (Luoyang Zhongda) using the procedure described in U.S. Pat. No. 6,231,784.

Strip Wt % Extract [Cu] [Cu], Net Cu Modifier modifier (gpl) (gpl) Transfer (gpl) 2,2,4-Trimethyl-1,3- 27 4.60 1.76 2.84 pentanediol (TXIB) Pentaerythritol 27 4.34 1.39 2.95 tetrapropionate

The improved copper transfer of the aldoxime formulation using a tetrapropionate ester modifier compared to the corresponding TXIB formulation, the most commonly used commercial modifier, demonstrates the utility of this invention. Copper mines using the new modifier will have improved copper recovery and require less of reagent in their process.

While various embodiments have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention. 

1. A solvent extraction composition, comprising: an orthohydroxyaryloxime extractant; at least one water immiscible organic solvent; and an effective amount of a substantially water insoluble equilibrium modifier selected from the group consisting of aliphatic, aromatic, and araliphatic compounds, the equilibrium modifier comprising three or more ester functional groups.
 2. The composition recited in claim 1, wherein the orthohydroxyaryloxime extractant comprises a compound according to Formula (1):

and salts, tautomers or metal complexes thereof, wherein R¹ is an optionally substituted C₁-C₂₀ hydrocarbyl group and R² is an optionally substituted C₆-C₂₀ orthohydroxyaryl group.
 3. The composition recited in claim 1, wherein the orthohydroxyaryloxime extractant comprises a compound according to Formula (2):

and salts, tautomers or metal complexes thereof, wherein R³ is an optionally substituted C₆-C₂₀ orthohydroxyaryl group.
 4. The composition recited in claim 1, wherein the orthohydroxyaryloxime extractant comprises a compound selected from the group consisting of: 5-(C₈ to C₁₄ alkyl)-2-hydroxyacetophenone oximes, 5-(C₈ to C₁₄ alkyl)-2-hydroxybenzaldoximes, and mixtures thereof.
 5. The composition recited in claim 1, wherein the equilibrium modifier comprises up to 80 carbon atoms.
 6. The composition recited in claim 1, wherein the ester functional groups are selected from butyrates, propanates and mixtures thereof.
 7. The composition recited in claim 1, wherein the equilibrium modifier is selected from the group consisting of trihydroxy alcohols, tetrahydroxy alcohols, polyhydroxy compounds, tricarboxylic acids, tetracarboxylic acids and mixtures thereof.
 8. The composition recited in claim 1, wherein the equilibrium modifier comprises a trihydroxy alcohol.
 9. The composition recited in claim 8, wherein the trihydroxy alcohol comprises up to 20 carbon atoms and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms.
 10. The composition recited in claim 8, wherein the trihydroxy alcohol is selected from the group consisting of: glycerol; 1,1,1-tris(hydroxymethyl)propane; 1,1,1-tris(hydroxymethyl)ethane; 1,2,6-hexanetriol; 3-methyl-1,3,5-pentanetriol; 1,3,5-triazine-2,4,6-triol; 1,2,4-butanetriol; 1,3,5-trihydroxybenzene; pyrogallol; and isomers of these compounds.
 11. The composition recited in claim 1, wherein the equilibrium modifier comprises a tetrahydroxy alcohol.
 12. The composition recited in claim 11, wherein the tetrahydroxy alcohol comprises up to 20 carbon atoms and a optionally substituted monocarboxylic acid containing 1-20 carbon atoms.
 13. The composition recited in claim 11, wherein the tetrahydroxy alcohol is selected from the group consisting of pentaerythritol and erythritol.
 14. The composition recited in claim 11, wherein the equilibrium modifier is pentaerythritol tetrapropionate.
 15. The composition recited in claim 1, wherein the equilibrium modifier comprises a polyhydroxy compound.
 16. The composition recited in claim 15, wherein the polyhydroxy compound comprises 5 or more alcohol functional groups having up to 40 carbon atoms and an optionally substituted monocarboxylic acid containing 1-20 carbon atoms.
 17. The composition recited in claim 15, wherein the polyhydroxy compound is selected from the group consisting of dipentaerythritol, carbohydrates and carbohydrate polyols.
 18. The composition recited in claim 17, wherein the polyhyroxy compound is selected from the group consisting of monosaccharide, disaccharide, oligosaccharide and polysaccharide.
 19. The composition recited in claim 15, wherein the equilibrium modifier comprises a mixture of at least one carbohydrate and at least one carbohydrate polyol, mannitol, sorbitol, xylitol, lactitol, maltitol, erythritol, isomalt, 1,6-GPS, 1,1-GPS, 1,1-GPM, hydrogenated starch hydrolyzate, hydrogenated glucose syrup and mixtures thereof.
 20. The composition recited in claim 19, wherein the equilibrium modifier comprises a carbohydrate polyol selected from the group consisting of a C₅-polyol, a C₆-polyol and mixtures thereof.
 21. The composition recited in claim 19, wherein the equilibrium modifier comprises a disaccharide polyol.
 22. The composition recited in claim 21, wherein the disaccharide polyol is selected from the group consisting of arabitol, xylitol, ribitol, inositol, mannitol, sorbitol, galactitol, and mixtures thereof.
 23. The composition recited in claim 1, wherein the equilibrium modifier comprises a tricarboxylic acid.
 24. The composition recited in claim 23, wherein the tricarboxylic acid comprises up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms.
 25. The composition recited in claim 23, wherein the tricarboxylic acid is selected from the group consisting of: benzene-1,2,4-tricarboxylic acid; trimesic acid; tricarballylic acid; aconitic acid; and mixtures thereof.
 26. The composition recited in claim 1, wherein the equilibrium modifier comprises a tetracarboxylic acid.
 27. The composition recited in claim 26, wherein the tetracarboxylic acid comprises up to 20 carbon atoms and a monohydroxy alcohol containing 1-20 carbon atoms.
 28. The composition recited in claim 26, wherein the tetracarboxylic acid is 1,2,4,5-benzenetetracarboxylic acid.
 29. The composition recited in claim 1, wherein the equilibrium modifier compound comprises alcohol functional groups that have been ethoxylated, propoxyated, or ethoxylated and propoxylated.
 30. The composition recited in claim 1, wherein the equilibrium modifier has a ratio of carbon atoms to ester functional groups of from about 7:1 to about 3:1.
 31. The composition recited in claim 1, wherein the equilibrium modifier has a ratio of carbon atoms to ester functional groups of from about 6:1 to about 4:1.
 32. The composition recited in claim 1, wherein the equilibrium modifier comprises at least one ether or alcohol functional group and has a ratio of carbon atoms to oxygen atoms of from about 3.5:1 to about 2:1.
 33. The composition recited in claim 1, wherein the molar ratio of the orthohydroxyaryloxime extractant to the equilibrium modifier is at least about 0.02.
 34. The composition recited in claim 1, wherein the molar ratio of the orthohydroxyaryloxime extractant to the equilibrium modifier is not greater than about 1.5.
 35. The composition recited in claim 1, wherein the composition comprises from about 1 wt. % to about 70 wt. % of the orthohydroxyaryloxime extractant.
 36. The composition recited in claim 1, wherein the composition comprises at least about 5 wt. % and not greater than about 30 wt. % of the orthohydroxyaryloxime extractant.
 37. The composition recited in claim 1, wherein the orthohydroxyaryloxime extractant comprises a mixture of aldoxime and ketoxime, and wherein the weight ratio of the aldoxime:ketoxime is from about 90:10 to about 30:70.
 38. The composition recited in claim 1, wherein the organic solvent has an aromatic hydrocarbon content of not greater than about 30 wt. %.
 39. The composition recited in claim 1, wherein the organic solvent has an aromatic hydrocarbon content of not greater than about 23 wt. %.
 40. The composition recited in claim 1, wherein the composition comprises from about 30 wt. % to about 95 wt. % of the organic solvent.
 41. The composition recited in claim 1, further comprising an anti-degradation additive.
 42. The composition recited in claim 41, wherein the composition comprises from about 0.1 wt. % to about 10 wt. % of the anti-degradation additive.
 43. A process for recovering a metal from an aqueous solution, comprising the steps of: contacting an aqueous solution containing a metal with a solvent extraction composition recited in claim 1, thereby forming a metal-solvent extractant complex in a water-immiscible phase; and contacting the metal-solvent extractant complex in the water-immiscible phase with an aqueous acidic strip solution, thereby stripping the metal from the water-immiscible phase.
 44. The process recited in claim 43, wherein the aqueous solution is an acidic solution.
 45. The process recited in claim 43, wherein the metal is chosen from the group consisting of copper, iron, cobalt, nickel, manganese, zinc and mixtures thereof.
 46. The process recited in claim 43, wherein the volume ratio of solvent extractant to aqueous acidic solution is from about 20:1 to about 1:20.
 47. The process recited in claim 43, wherein the volume ratio of solvent extractant to aqueous acidic solution is from about 5:1 to about 1:5.
 48. The process recited in claim 43, further comprising the step of recycling the solvent extractant or the aqueous acidic solution.
 49. The process recited in claim 43, wherein the aqueous acidic strip solution is a mineral acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid and mixtures thereof. 